Phase and amplitude modulation receiver



Oct. 29, 1935.

M. G. CROSBY Y THSE AND AMPLI'IUDEv MODULATTO RECEIVER 5 Sheets-Sheet l.

Filed April 9*. 1954 INVENTOR M. 6. C RO SBY ATTORNEY 5 Sheets-Sheet 2 yM.`G.cRosBY PHASE AND AMPLITUDE MODULATION RECEIVER Filed April 9. 1934ATTORNEY 5 Sheets-Sheet 3 M. G. CROSBY Filed April 9. 1954 PHASE ANDAMPLITUDE MODULATION REEIVER Oct. 29, 1935.

ATTORNEY PatentedY ocr. '29, 1935 UNITED STATES PHASE AND RECEIVERMurray'G. Crosby, Riverhead, N. Y., assigner to Radio Corporation ofAmerica, a corporation .of

Delaware Application Aprile, 1934, `seriaiNu.''119.643 isoiaims. (o1.25o-go) This invention relatesv to anew and improved receiver which iscontantly' receptive to either a phase or an amplitude modulation on thecarrer wave or to both. The purpose of this re- 5 ceiver is to eliminatethe vdefects present in receivers'known heretoforeresulting from fadingof the wave ormulti'V-path transmission of the wave which in turncauses-distortion ofthe wave modulations from an amplitude modulation toD a phase modulation, or from a phase modulation to an amplitudemodulation. Brieily, my inven' tion contemplates the use of a receiverwhich is adapted to demodulate amplitude modulated Waves and isalsoadapted to demodulate phase i modulated waves anda switching' deviceorga modulating `device for constantly changing the characteristics ofthe receiver at a super-audible rate so that the receiver is alternatelyresponsive to either phase or amplitude modulation.

r In the pri r art in general, the reception of l signal modulated Wavesis accomplished by means of receivers which are receptive only to thetype of modulation impressed on the wave at the transmitter.Consequently in these receivers of the prior art, if for anyreasonwhatever the f nature of the modulation on the waveis changed ordistorted so that itdeviates from that type of modulation accomplishedby the transmitter the receiver of distorting a modulated wave from onetype of modulation to another, that is from amplitude modulation tophase modulation or vice versa, such a condition of modulationconversion is one which is common and a receiver which will receive boththe applied modulation and the modulation to which the appliedmodulation may be distorted or converted is valuab1e.`

The receiver of the present invention eliminates the above describeddefect by providing demodulators operative to render amplitudemodulations from carrier energy or to render phase modulations fromcarrier energy. One demodulator is therefore capable of demodulating themodulation intentionally applied at the transmitter and the otherdemodulator is capable of rendering the type of modulation to which thefading or other eiccts converts the applied modulation. v

Thus by switching first one demodulator on and then the other, at asuper-audible rate, the desired signal will be constantly rendered anddelivered from the receiver.

In a modification one demodulator onlyis utilized and its operativecharacteristics is altered at an above audible rate so as to make thereceiver will not translate the signal wave from the carrier wave. Sincefading is capable alternately receptive tothe two types of modulattion.Y

' The novel featuresof my `invention have been., pointed outwithparticularity in the claims at'.

, the end ofthe specification. The naturevofinyr 5 invention and themanner in which the same is carried outv will be clearfror-nthefollowing -detailed description thereof and therefrom when v read inconnection with the attached drawings throughout which insofar aspossible like refer- 1o ence characters indicate like parts and in whichFigures 2 to 4 inclusive illustrate various modivcations of my novelreceiver invwhich 'a pair of demodulators of different types arerendered operat'ivet at a super-audible rate; i 15 Figure lril'lustratesa modification wherein a single, demodulator is utilized and thedemodulat.. ing characteristic ofthe Asame is altered at a super-audiblerate; .i

AWhile Figure 5 is a graphic representationof 20` the manner inwhichlthe demodulators of Figures 2, 3 and4 4 are alternately,rendered'operativey and ofthe manner in which the characteristics of thedemodulator of Figure 1 is changed."k

Referring to the drawings, and in particular-to 25 Figure 1 thereof, aradiant energy absorption dee vice I is` connected as shown with areceiver 2 of the'superheterodyne type. .The receiver 2 ymay includeradio frequency ampliers, a source of local oscillation, a demodulatorand an inter- 3o mediate frequencyamplier. 'Ihe receiver 2 converts theincoming signal modulated energy to an intermediate frequency andimpresses the same on the lines 3 and 4. Part ofthe intermediatefrequency energy from 2 is passed by way of lines 35 4 to theprimarywinding of a co-,phasal transformer l0. The secondary winding of thetransformer I0 isl connected as shown to,l apply the energy set uptherein co-phasally to the control grids of demodulators Il and l2.Another por- 40 tion of the'intermediate frequency energy from theoutput of 2 is. passed by wayof ylines -3 to a unit 5 which may includea. filter of the crystal or any other type and an amplitude limiter oran automatic volume control, The frequency 45 limited and amplitudelimited energy from the output of unit 5 is impressed on a unit'6 whichmay include a phase adjusting device. The en" ergy from the output ofthe phase adjusting device is impressed on a phase modulator ,'l. The450 phase of the energy in 1 is modulated by oscillations from thesource8.` The frequency of the oscillations from the source 8 should beaboveaudibility. The energy from the output; of the phase modulator 'l isapplied to the primary wind- 65 Aas "anti-phasally by the transformer 9.The output electrodes of the demodulators II and I2'may be connected asshown to the primary winding of a transformer I3, thesecondary windingof which may be connected with a jack I4 in which any indicating devicemay be inserted. The phase modulator 1 and source `8 may of course bere- -placcd by any means for shifting the phase of the energy in 1substantially 904 degrees at an above audible rate 'i In themodification shown in Figure 2 two separate demodulating devices may beutilized. The transmitted energy may be received on an absorption memberI and a superheterodyne receiver 2 and applied to thelines 3 and 4in-the same manner as inthe arrangement of Figuie 1. A portion'of theenergy isifed by way of line 3 to the lter and amplitude limiter in 5andthe frequency limited and amplitude limited energy from the output of5 is impressed. on a line or phase shifter device l5 comprisingseriesinduc` tive reactances and parallel capacitive reactancesterminated by an impedance; Energy of the desired phase relation istaken from the line by means of leads L connected as shown to movabletaps on the line I5. The energy diverted from the line I5 by the `leadsL is applied to the control grids of modulator tubes I6 and I1 as shown.The modulators I G and I1 may be of the screen grid electrode type andmay havetheir screen grids connected as shown by way of radio fre.

quency by-pass networks RFC to the terminals of the secondary` windingof a transformer I8, the primary windingpf which is connected with asource of modulating potentials I9. A direct current charging potentialfor the screengrid electrodes is provided by means of a source Sconnected as shown. The anode of the modulatorl I6 is connected to thecathode thereof by way of the primary winding of a transformer rI' and asource S1. The anode electrode of `thernodulator I1 is connected tothecathode by way of the primary winding of a transformer T1 and sourceS1. The secondary winding of the transformer T connects as shown thecontrol grids of a pair of detector tubes 20 and 20 in pushpullrelation. The secondary winding ofthe transformer T1' connectsthecontrol grids of a second pair of detector tubes 2| and 2| in`push-'- pull relation. Intermediate [frequencyA energy from thesuperheterodyne receiver is fed by Way of line 4 to the primary windingsof transformers 28 and 29. The secondary Winding of transformer 28`applies this energy co-phasally, that is, in phase to the control gridsof tubes 20 and 20. The secondary winding of transformer'29 appliesenergy co-phasally to the control grids of detectors20 and 2I The anodeelectrodes kof tubes 20 and 20 are connected .in pushpull relation bythe primary winding of a transformer 22 while the anode electrodes oftubes 2l and 2| are connected in pushpull relationby the primary windingof a transformer 23. The energy from the outputs of both pairs `ofdetectors are combined by connecting the secondary windings oftransformers 22 and 23,'together as shown. The combined energy may beapplied to anyindicating device from the jack I4.

In the modification of Figure 3 the demodulators of the arrangement ofFigure 2 are replaced by multi-grid detectors. The signal, after beingconverted to intermediate frequency wave energy, is fed by way of lines4 to the primary winding of a, transformer 30, the secondary winding ofwhich is connected to the control grids of detectors 26 5 and 21 asshown to apply energy to said control grids in phase. A second portionof the inter- 'mediate frequency energy is fed by way ofv the 11tercircuitsgandvamplitude limiters in 5 to a line 3l, which is connected asshown to the in- 10 puts of a pair of phase Shifters 24 and 25 whoserespective outputs feed energy by way of transformers 33 and 34 to thesuppressor grids of dey\tectors 26j and 21 respectively., A modulatingfrequency generator 36 is connected asshown by l5 Way of transformer 35to the screen electrodes of detectors 26 and 21 to modulate thepotentials on screen grid electrodes alternately at an aboveaudible.frequency rate. The anode electrodes'of'detectors 26 and 21 areconnected as 20 shown by way of resistances and capacities to thecontrol grids of'amplifiers 4U and 4I. The

` anodesof ampliers 4u and 4I are connected in pushpull relation bythey' primary winding ,of

`they'rnay takev the'formof the line I5 shown in Figurev2'. Inglthemodification of'Figure 4, energy from the intermediate frequency'amplifier is fed by waygv of a line 44 to'an upper side-band filter 35and by'way-.of'a line 45 to a lower side-,band

transformer 43, the secondary of which is con- 25 'filter 36:11 lEnergyfrom the output of the upper 35 side-band filter 35 is supplied to thecontrol grid of a demodulator 4B while energy from the lower outputofthe lower side-band 36- is supplied tov the control grid `of ademodulator 41.

The signal components of the demodulated waves 40 are supplied from theoutput of detector 43 by Way of a transformer 49 to a coupling tube 5I.Energy from the output of the detector 41 is supplied to the primarywinding of a transformer 52, the secondary winding of which is connected45 in pushpull relation to thecontrol grids of couv pling tubes 54 and55 as shown. The screen grid electrodes of 'coupling tubes' 54 and 55are connected inphase opposition as shown to the secondary winding of atransformer 51, the pri- 50 mary winding of which is connected to asource of modulating potentials 56. f Modulating potentials from thesource 56 are superimposed in phase opposition on the direct currentpotential applied to the screen grid electrodes of tubes, 54 55 and 55from source 58. These superimposed modulating potentials render the'tubes 54 and 55 alternately operative to supply energy to their outputcircuit. anodes of tubes 54 and 55 are connected as shown in parallelwith the primary winding of a transformer 44, thev secondary winding ofwhich is connected with a jack I4 from which the signal components maybe applied to any indicating device.

In describing the operation of the receivers of K The anode of tube 5Iand the f The receiver of Y bands are removed and after limiting theamplicombined with the unfiltered signal applied to the controlelectrodes of Il and I2 in the proper phase relationship. For'phasemodulation reception the lter carrier is adjusted in 6 so as to beshifted 90 vdegrees with respect to the unltered energy' applied by wayof lines 4 to the primary winding of transformer I Il and thence inphase to the control grids of II and l2. This combination in phasequadrature of the limited and fil tered" and unltered signal energyproduces ainplitude components which vary `in accordance" with thevariations in phase of the unltered energy. For amplitude modulationreception the carrier applied to the control grids of modulators I I andI 2 should be either in phase or 180 degrees out of phase with respect'to theunltered signal energy reaching the control grids of thedemodulators I I and I2 from the line 4. Obviouslyif means is providedfor'shifting thephase of the iiltered carrier energy reaching thecontrol grids of the demodulators so that at one instant said `carrieris shiftedSQ degrees with respect'tothe `unltered carmen-andthe nextinstant said lil-,- tered carrier is shifted in phase or 180 degreesy,

out of phase with respect to the unfiltered carrier, the receiver willbe responsive to both phase and amplitude modulated waves. Consequently,if fading distortion is such that it distorts the modulation applied tothe wave in the transmitter from amplitude to phase modulation or viceversa correction may be made in my novel receiver by varying the phaseadjustment of the filtered carrier. In order 'to ymaire manualadjustment of the iiltered carrier phase unnecessary, the phasemodulator of unit 1 is included in the line between the carrier iilter 5and the demodulators II and I2. This demodulator is capable ofmodulating the-` carrier over a range of 90 degrees in phase. 'I'he rateof modulation is determined by the tone generator 8 which may have asquare wave form so that the phase of the carrier will be shifted fromplus 45 to minus 45 degrees, as shown in Figure 5. At plus 45 degreesthe-receiver will then be adjusted for phase or amplitude modulation andat minus 45 degrees the receiver will be receptive to amplitude or phasemodulation respectively. Hence, by means of the phase modulatorthereceiver may be switched so that it is alternately receptive'to phase oramplitude modulation for ,equal intervals of time determined by thenature of the oscillations generated by 8. Such an arrangementeliminates the necessity of a receiver receptive to either type ofmodulation one-half the time and prevents fading distortion on eithertype of modulation from distorting the signal in the output of thereceiver or from preventing the signal from reaching the output of thereceiver. The rate of switching may be made super-audible so that themodulation due to the switching action is not objectionable.

The principles of reception described above in connection with Figure 1are applicable to the modiiications shown in Figure-2. In Figure 2,however, two sets of detectors are utilized. One set of detectors may beadjusted to receive phase modulation while the other set of detectorsmay be adjusted to receive amplitude modulation.

vMore specifically the unfiltered carrier from line 4 may be applied tothe control grids of detectors 20 and 20 in 90 degrees phase shiftedrelation with respect to the ltered carrier supplied to the controlgrids of detectors 20 and 20 from the modulator tubes I6 and I1, whilethe unltered screen grid electrodes.

vto phase modulated tubes 2| and 2| in phase'or 180 degreesout of phasewith respectto the filtered carrier applied to the control grids ofthese tubes from themodulators I6 and I1. The tubes I6an`d/l1-are `5modulated on their screen grid electrodes in such a manner that energyis fed from modulators I6 and I1 so that first one set of thesedetectors gets carrier, energy and then the other set of lthesedetectors gets carrier energy. The output cir- 10 cui-ts of the two setsof detectors are connected to combine the energy sothat whicheverdetector islswitched on, that detector will supply signal'to' the jacki4 and any indicator connected therewith. Consequently the receiver is15 alternately receptive to 'either phase or amplitude modulation andsaid receiver will eliminate the effect ofm'odulation distortionlin thesame manner in which said distortion is eliminated by a receiver asillustrated in Figurel. 'I'he 20 f generator -I9 may havel a square Waveformso that the interval during which each receiver is alternatelyinoperative is short whilethe interval during which each receiver isoperative is comparatively long. Furthermore, the modulations 25produced by I 9 may be audible or may be superaudible.- v1" f` In thereceiver of Figure 3, which isotherwise similar in many respects to thereceiver of Figure 2, multi-grid detector tubes are used asl shown.These detectors are rendered alternately operative and inoperative atthe desired rate by mod ulating the screen grids differentially bymodulating potentials applied from .the'modulating potential source byWay of transformer to said 35 Phase shifter -24 may be adjusted so thatthe demodulator 26 is receptive waves. Phase shifter 25 may be adjustedso that vthedemodulator 21 is receptive to amplitude modulated waves.When 40 the tone generator mayhave a square wave form and may operate ata super-audible rate.

The receiver shown in Figure 4 may be some.- what similar in somerespects to the receiver disclosed in Crosby United States applicationNo. 616,803, filed June 13, 1932. Heretheupper side- 5 5 band of theintermediatefrequency wave is filtered out and applied to a detector 46as shown,

`while the lower-side-band isiiltered out and applied to the controlgrid electrode of a detector 41 as shown. If energy' from the outputs ofthese 60 detectors is vcombined'in phase the receiver yis receptive toamplitude modulation. If energy in I the output `of the detectors 46 and41 is combinedr in phase yopposition the receiver responds toaI phasemodulatedwave.

modulating means 56., 51, 58 connected with the screen grids-ofcouplingtubes 54and 55 as shown is operative to switch from out-of-phase combination ofput energy, the receiver both types of modulation. Themodulating means and the single detector 5I and' the pushpull detectors54 and 55 as -connected will couple the output of 46 and 41 alternatelyin an inphase and an out-of-phase relation. If the o ut- 75 an vin-phaseto an the detector out- Consequently, if the will -be responsive to putsof the coupling tubes 5l and 54 are combined, an in-phase combinationresults, so that the receiver is responsive to amplitude modulatedwaves. If the energy from the outputs of tubes 5l and 55 are combined,an out-of-phase combination results and the receiverl is responsive tophase modulated waves. Hence by differentiallymodulating tubes 54 and 55so that first one tube is inoperative and then `the other, the desiredswitching effects are obtained and the receiver is responsive to phasemodulated waves or amplitude modulated waves. I,Hermes in the priormodifications, the source of modulating potential 56 may produce waveshaving a form as illustrated in Figure 5. Moreover, the frequency e ofthese waves may be above or below audibility.

Automatic frequency control may be applied to each of the receiversdescribed above. Such frequency control means may be as illustrated inCrosby United States application No. 616,803, filed June 13, 1932. Thefrequency control means per se forms no part of the present inventionand need not be described here.

The principle involved in these receivers may, of course, be applied todiversity reception systems. In the receiver of Figure 2 the signalenergy may be switched instead of the carrier energy. This may beaccomplished by placing the modulatorA tubes I6 and I1 in the lines 4which feed the signal energy to the detectors instead of as shown in thelines feeding the carrier energy to the detectors.

Having thus described my invention and the v operation thereof, what Iclaim is :1

1. In a systemv for receiving and demodulating oscillations modulated inphase and in amplitude, a signal absorbing means, signal amplifyingmeans coupled thereto, signal demodulating means coupled by circuits tosaid signal amplifying means, and means connected with one of saidcircuits for rendering said demodulating means receptive to differentAtypes of signal modulations.

2. In a system for receiving and demodulating oscillations modulated inphase and in amplitude, signal absorbing and amplifying means, aplurality of signal demodulating means responsive to signal modulationsof different character each coupled by a plurality of circuits ofdifferent character to said signal amplifying means, and means in one ofsaid circuits for alternately changing the character of the energyflowing therein to said demodulating means.

3. In a system for receiving and demodulating oscillations modulated inphase and in amplitude, signal absorbing and amplifying means, signaldemodulating means coupledl by two separate circuits to said signalamplifying means, and means in one of said circuits for modulating thephase of the energy reaching said demodulating means over one of saidcircuits.

4. In a system for receiving waves modulated in amplitude or in phase orboth,`signal` modulated wave absorbing means, a device for reducing thefrequency of said Wave connecting with said absorbing means,demodulating means comprising a'pair of thermionic tubes, a circuit forapplying energy from said Wave reducing vmeans co-phasally to the likeelectrodes in said tubes, a circuit for applying energy from said wavereducing means in phase opposition to like electrodes in said tubes anda deviceiin one of said circuits for varying the character of the energytherein.

5. In a system for receiving waves modulated in amplitude or in phase orboth, modulated wave absorbing means, a device for reducing thefrequencyof said wave connecting with said absorbing means, demodulatingmeans comprising a pair of thermionic tubes, a circuit for applyingenergy from said wave reducing means co-phasally to the like electrodesin said tubes, a circuit for applying energy from said wave reducingmeans in phase opposition to like electrodes in said tubes, a filter inone of said circuits, and a 10 device in one of said circuits forvarying the character of the energy flowing therein at a subaudiblerate.

6. In a system for receiving waves modulated in amplitude or in phase orboth, modulated wave H absorbing means, demodulating means comprising'apair of thermionic tubes, acircuit for applying energy from saidabsorbing means c0- phasally to the like electrodes in said tubes, acircuit for applying energy from said wave absorbing means in phaseopposition to like elec-. trodes in said tubes and a device in one ofsaid circuits for modulating the energy therein at an above audiblerate.

rI. In a system for receiving and demodulating oscillations modulated inphase or in amplitude, signal absorbing means, signal amplifying means,a lter circuit connected with said amplifying means, differentialdetectors each comprising a control grid, a circuit for applying energyfrom said amplifier in phase to said control'grids,

a circuit 'for applying energy from said amplier in phase opposition tosaid control grids, said last named circuit including a filter forremovv ing the signal modulations from the energy, and means in saidlast named circuit for modulating the phase of the ltered energyreaching the control grids of said detectors in phase opposition. 8. Ina system for receiving and demodulating 40' oscillations modulated inphase or in amplitude, signal absorbing means, signal amplifying means,

a filter circuit connected with said amplifying means, differentialdetectors each having control grids, a circuit for applying energy fromsaid l amplifier in phase to like control grids of said tubes, kacircuit for applying energy from said amplier in phase opposition tolike control grids of said tubes, said last named circuit including afilter for removing the signal modulations from the energy, and means insaid last named circuit for varying the phase of the filtered energyreachingthe control grids of said detectors in phase opposition through90 degrees. 9. In a system for receiving and demodulating 55oscillations modulated in phase or in amplitude, signal absorbing means,signal amplifying means, a pair of differential detectors eachcomprising a control grid, an, additional detector tube, circuitsconnecting the outputs ofall of said detectors together, a circuit forapplying energy from said amplifier to the control grids of said pair ofdetectors, a circuit for applying energy from said amplifier to thecontrol grid of said single detector, said circuits each including alter and means for ,rendering the differential detectors alternatelyoperative at a super-audible rate. l0. In a system for receiving wavesmodulated in amplitude or in phase or both, modulated wave absorbingmeans, a device for reducing the frequency of said wave connecting withsaid absorbing means, wave demodulating means comprising a pair ofthermionic tubes each having a plurality 'of control electrodos, acircuit for applying en- 40 nal modulations from the Vwave energy, and

modulating means in said last named circuit forv to like controlelectrodes in said/tubes, other circuits for applying energyrom saidwave re- 'ducing meansto like control-electrodes in said trodes in saidtubes. 1

A 11. In a system-for receiving and demodulating oscillations modulatedin phase or in ampli'- tude, signal absorbing fmeans, signal amplifyingmeans, 'anlter circuit connected `with said. ampli-f` lli `fying, means,two .sets of .diilerental detectors j" 'Veajchf detector ofeachjsethaving a control grid,

a circuit forapplying energy 'from said amplifier in like phase.tof'the' icontr'l grids in each 'set of detectors, a circuitfforapplying energy',from gn .I .said filter in phase Hoppositien' :'to the'm'.pntrol-v`v 1 H igrids in each set "of detectors, means in saidlast20l v teredenergy reaching of said sets of detectors substantiallyninety d grees relative tothe energyreachi'ngthecontrol 1 grids of saiddetectors from saidamplifejr,means,. for alternately increasing anddecreasing the energy reaching said sets of detectors oversai'dh lastnamed circuit, and an output circuit connected to the output of all ofsaid detectors. A 12.' In a system for receiving and demodulat-` ingwaves modulated in phase or in amplitude,`

named circuit for shiftingthe-"phase cfthe-.fil-

thecontrol grids of one signal wave absorbing means, signal wavefrequency reducing means connected with said signal wave absorbingmeans, a lter circuit con-v nected with said reducing means,,diierential detectors each comprising a control grid, a circuit forapplyingI energy from said reducing means in'phase to said controlgrids, a circuit for applying energy from said reducing means in phase jopposition to said control grids, said last named circuit including saidlter for removing the sigshiftingthevf phase of the ltered energyreachingthe control grids of said detectors in phase opposition throughsubstantially 90 degrees.

13. 'I'he method of eliminating the eiect of fadingv on a signalmodulated Wave, which fad- Y -ingtends to change theA character of thesignal modulation on said wave whichis'being received -on a receiverhaving a demodulator Vwhich in-- cludes the stepof, and supplyingenergyfrom said` -wave`tosaid demodulatonoyei two pathschangingthe:demvgiclulation characteristic of said demodulator byshifting the phase ofthe energy -l suppliedover one of said paths atamper-audible Y ff-rate. f

A14. The method of eliminating the distortion I' caused in thedemodulation of a signal-wave,

due .to the tendency of said modulation to change transmissionofthewave, which is to be received from one type of modulation to anotherduring lquency on 1 energy 'characteristic ofl said lwave. in 'phase ony A the control gridsof .said pair of differex'itialv detectors over one.path andrin -outeof-phase jrela- `5 `tion on saidcontrollgrids overanother path,l andl g modulating the --ph'aseof` one vof Vsaidl energiesa reaching said control'gridsover-one of said paths through 9oldegreesat -anabqve guaine rate.

steps;',of,V amplifying -said wave, ll nersi'lfof "said wave te removethere-- odulatlon"thereon,.applying said filed nergyAinyphasejoppositionvtoY-the control gridsjof[said` detectors, applying other energy 20haracteristic'jof'- the-modulation on said wave in .phszto Athe]'control @grids of; said detectors, and

-mddlllatinsone ofsafid' energies ata super-audible rtef 11.6.?. ,Meansder 'eliminating theeffectof fading 25 fon-"ja.signal-modulated-wavewhich tends to change-the typ? .Of `IIlodulationon' said kwave compris'ing*signalabsorbing means, signaldemodulatin'glmeans,aV plurality of circuits connecting said absorbingmeans to said demodulating 30 means, andvphase modulating means in oneof said circuits for changing thencharacteristic of said demodulator ata `super-audible rate.

Y1'7. In means for eliminating-,the distortion caused in thedemodulation of ya carrier wave due to the tendency of said. modulationto change from one'type of modulationto another during transmission ofthe wave,"`a'demodi1lating device, means for impressing'signal modulatedenergy fromsaid carrier Wave von'said (levied-means 40 for impressingunmodulated energy characteristic of said carrier wave onjsaidf deviceand means for shiftingy the phase of lone oflsaidenergies before thesame is impressedlon said device through 90 degrees at an above audiblerate. r

18. The method;` yof eliminating, theeilect of distortion on van"-arnplitude* modulated wave which y-tends to vchange, the'same to phasemodu- .lation'when said-wave is received on a receiver including apain-of differential detectors which tional energycharacteristic of themodulations on Vsaid wave inphase to the control `grids of saiddetectors, and ,modulating one of saidf'energies reaching-said fcontrolgrids atza super-audible on a receiver including a pairof differentialde. v' -tectors which includes the steps-of, kimpressing

